What is the Dunning-Kruger effect?

The effect is named after psychologists David Dunning and Justin Kruger of Cornell University, who published the study 'Unskilled and Unaware of It' in 1999. In tests of logic, grammar and humour, participants who scored in the bottom quarter, averaging around the 12th percentile, estimated that they had performed at about the 62nd percentile. The researchers argued that the skills needed to do a task well are the same skills needed to recognise good performance. They were partly inspired by a 1995 case in which a bank robber believed lemon juice would make his face invisible to cameras. Some later researchers argue part of the effect can be explained by statistical artefacts, so it remains debated in detail.